U.V. Sterilizers for the Pond
by Richard Renshaw
Ventura County Koi Society
One of the fastest growing products for a Koi pond is the ultra-violet (U.V.) sterilizer. The
ultra-violet sterilizer is a device which uses U.V. light to kill micro-organisms in
water. U.V. light bulbs look like a fluorescent light bulbs. Ultra-violet disinfection has
been used for many years in hospitals and in water purification. There are even
units made for sanitizing spa and hot tubs. The aquarium hobbyists have U.V.
sterilizers available for delicate aquarium setups. The Koi hobby has known about
U.V. for over 10 years, but have not accepted the technology until now. The
reason is, there is some confusion as to what to expect. A U.V. unit is not meant to
replace a bio-filter. You still need a bio-filter for removing the ammonia wastes.
You should not expect the U.V. unit to sterilize your pond. There will be bacteria
on and in your fish, in the biological filter bed, and on the walls and bottom of the pond.
What you can expect is to control harmful bacteria, algae, and other waterborne
microorganisms by reducing their numbers. The trick is not to destroy all the
organisms in one cycle. But, to expose the unwanted organisms to repeated small
doses over a period of time. With this in mind, you will need a 500 - 1500 GPH
flow rate for a 15 - 50 watt U.V. unit. If your flow rate is greater, you can install a
"tee" before the U.V. sterilizer and bypass the excess flow around the unit. When
using a "tee", have the main flow directed straight into the U.V. unit and the bypass
coming off the existing straight pipe. That way you will get maximum flow
through the U.V. unit. Since some of the U.V. sterilizers are designed for other
applications, it is important to know what to look for:
In conclusion, U.V. sterilizers do work, but they are expensive. Be aware of poorly
designed equipment. Usually a normal sterilizer unit looks like a 3 inch white pvc
pipe with inlet/outlet connections on the side at each end and a U.V. tube running
through the center. The ends of the tube (U.V. bulb) will be sealed with o-rings and
the wiring connections covered with rubber boots.
If ultraviolet sterilizers sound interesting, and you are looking for a source for good
pond quality U.V. units:
- The unit should be designed for outdoor use or be provided with a suitable enclosure.
Electrical supply should be protected with a G.F.I.
- The unit should have an effective and efficient design. U.V. lamps that are surrounded by
water are much more efficient than a lamp suspended over water. U.V. light does not behave like
visible light. For example, it does not pass through normal glass or transparent plastic, and it
reflects badly from most surfaces (even mirror finishes).
- The U.V. sterilizer bulb must be surrounded by a quartz glass sleeve. A U.V. bulb normally
operates at 72 degrees Fahrenheit or above. The special quartz sleeve allows the bulb to operate
in colder water at its normal temperature for maximum performance. U.V. bulbs have a limited
effective life of 7000+ hours. Bulbs should be changed at least every year.
- With efficient designed U.V. units, you will need about 10 bulb watts for every 1000 - 1200 gallons of pond.
For stubborn algae problems, you will need more light because algae is more resistant to U.V.
light and U.V. does not penetrate cloudy water and looses efficiency.
- The U.V. unit should be installed so that the bulb is surrounded by water, no air pockets.
- Aqua Art (more information on U.V.)
- 1341 Money Way
- St. Helena, CA 94574
- e-mail: firstname.lastname@example.org
- 5252 Lovelock St.
- San Diego, CA 92110
- Aqua Ultraviolet
- 43339 Business Park Dr. Ste 103
- Temecula, CA 92590
- For location of a dealer: 1-800-454-2725
- The Tropical Marine Centre Ltd
- Solesbridge Lane, Chorleywood
- Rickmansworth, Herts. WD3 5SX
- Tel: 09278 4151
Return to Koi Ponds and Filters
Copyright © 1996, Richard Renshaw, Revised March 15, 1997